A semiconductor device such as a power metal-oxide-semiconductor field-effect transistor (MOSFET) is widely used as a regulator or a switching element. For example, in a case where a wide trench is formed with a high breakdown voltage design, a film formation thickness of polysilicon is increased or deposition of the polysilicon is layered in two stages.
However, in such a structure, stress is increased and a warp of a wafer is increased. In addition, when a recess of the polysilicon of a gate electrode is formed, its shape becomes a mortar shape recessed in the center by dry etching, and in a case where a right above contact is formed, it is difficult to make a sufficient width to form a contact region in the gate electrode. Further, if a shape of the gate electrode is an acute angle in an insulating film interface separating a drain voltage and a gate voltage, electric field concentration tends to occur locally, and destruction of a gate insulating film is caused. On the other hand, if it is attempted to form the upper surface of the gate electrode flat, a process is required such as chemical mechanical polishing (CMP), and the number of manufacturing steps is increased.